The subject matter of the present invention relates to a premix burner arrangement and method for adding, enriching, or increasing the overall concentration of oxygen when combusting a mixture of air and a combustible gas such as natural gas.
Industrial furnace heating applications often employ burners operating with premixed air and fuel (e.g. Natural Gas). The reactants can be premixed, for example, at the stoichiometric ratio, which is sufficient for complete combustion. The main reasons for premixing fuel and air are: (i) simplicity and cost savings; only one pipe to the burner is needed instead of two for nozzle mixed burners; (ii) air-fuel flames are generally difficult to stabilize, especially in cold furnaces, so premixing helps with flame stability.
Premix air-fuel combustion is very difficult to enrich with oxygen. This is due to the potential of flame flashback and burner damage, if significant additional oxygen was added directly to the mixture of air and fuel. The potential of flashback has limited direct addition of oxygen to premix combustion mixtures to a relatively low level enrichment, e.g. 23% O2.
There are situations when combustion improvements are needed, such as for production increase, quality improvement, or fuel savings, where significant oxygen enrichment of such burners is considered. However, oxygen enrichment of premix air-fuel burners is not a simple matter. Additional oxygen is not directly “premixed” with the fuel because the speed of an oxy-fuel flame usually travels faster than the velocity of the “premix flow”. This results in a “flashback”, i.e., flame travels back through the premix flow pipe to the source of mixing increasing the potential of explosion. The flame speed is generally much lower for the air-fuel case which enables the premix type of operation.
U.S. Pat. No. 5,256,058, which is hereby incorporated by reference in its entirety, discloses an oxy-fuel burner that employs a precombustor between a burner and a process furnace. U.S. Pat. No. 5,199,866, which is hereby incorporated by reference in its entirety, discloses an adjustable oxy-fuel burner. Neither of these patents discloses a premix gas mixture, nor the low velocity injection of oxygen circumferentially around a central gas stream.
A premix burner arrangement, a combustion system, and method for enriching combustion of a pre-mixture of air and a combustible gas with significant additional oxygen that is safe, efficient and reduces or eliminates overheating of the burner components would be desirable in the art.